This application claims the priority of 198 25 591, filed May 5, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a transmission for motor vehicles, and more particularly, to a drivetrain for a motor vehicle (a) with a drive shaft and (b) an output shaft arranged coaxially with the drive shaft (c) with a continuously adjustable variator, which has two drive toroidal disks rotating together and two output toroidal disks rotating together, (d) with an epicycloidal gear train having two gears, that is at last one first sun gear and at least one planet gear supported by way of a planet carrier, (e) the drive toroidal disks or the output toroidal disks being torsionally fixed or connectable to the first sun gear of the epicycloidal gear train, and the disks (output toroidal disks; drive toroidal disks) that are not or cannot be connected to the first sun gear being torsionally fixed or connected by way of at least one planet carrier of the epicycloidal gear train.
DE 198 26 591 A1 discloses a transmission having an output shaft arranged coaxially with a drive shaft. A continuously variable adjustment of the transmission ratio is achieved by a toroid variator with two jointly rotating drive toroidal disks and output toroidal disks. The drive toroidal disks are arranged between the output toroidal disks. For further influencing the transmission ratio, the transmission has an epicycloidal gear train with a sun gear that rotates with the drive toroidal disks and a planet carrier that rotates with the output toroidal disks. The toroid variator is used for a forward gear, while a fixed transmission ratio is achieved for reverse gear. For achieving forward movement of the motor vehicle, the transmission has a starting element with hydrodynamic torque converter and lockup clutch.
An object of the present invention is to widen or improve the range of applications or functionality of a continuously variable transmission of compact construction.
According to the present invention, this object has been achieved by providing that a second planet gear moved by or with the first planet gear has a diameter such that for a transmission ratio of the variator at on operating point thereof the contact point of the second planet gear with an output element of the epicycloidal gear corresponds to the instantaneous centre of the second planet gear.
A second planet gear moved by or with the first planet gear has a diameter such that for a transmission ratio of the toroid variator at an operating point of the latter the contact point of the second planet gear with an output element of the epicycloidal gear train corresponds to the instantaneous centre of the second planet gear.
The toroid variator is a two-chamber variator with two drive toroidal disks and two output toroidal disks. As an alternative to the toroid variator, any variator that permits a continuously variable transmission ratio and has two drive toroidal disks and two output toroidal disks may be used. The two inside disks (drive toroidal disks or output toroidal disks) may be configured as one structural unit, for example as one disk with two running surfaces remote from one another.
The drive shafts and output shafts according to the present invention may be transmission input and transmission output shafts or input shafts or output shafts of a sub-division with further primary or secondary, direct or split-torque transmission stages of the vehicle transmission.
The epicycloidal gear train according to the present invention is a planetary gear train and/or an epicycloidal gear train with single planet gears, double planet gears (hereinafter also referred to as reversing gear train) or planet gears designed as stepped planet gears with or without internal gear and with one or more sun gears. A plurality of planet gears torsionally fixed to one another or intermeshing planet gears can be arranged in one or more planes. The planet carrier can support either one or more planet gears. The planet gears may be single or multiple planet gears depending, in particular, on the torques to be transmitted or the directions of rotation obtained. Each planet gear or each sun gear or individual sun gears or planet gears can mesh with one or more further gears.
The output element is preferably formed coaxially with the Xxe2x80x94X axis, for example as an internal gear or sun gear meshing with a (first) planet gear or a (second) planet gear moved by or with the former, to which internal gear or sun gear the rotational movement of the first planet gear is transmitted. The output element is connected directly or indirectly by way of further gear stages, transmission stages or couplings to the output shaft or gearbox output shaft.
The connections may be configured as (torsionally) fixed direct connections or as indirect connections, for example by way of further gear stages, or as detachable connections, which make a torsionally fixed connection only in specific operating conditions of the transmission. According to the present invention, the disks may be connected to one another directly or indirectly by inserting further components, especially shafts. This can be done by way of the planet carrier, for example, in which the power flow, especially for a torque transmission or transmission of axial force, passes by way of the planet carrier and any (hollow) shafts arranged on its input or output side in the direction of the power flow.
The arrangement according to the invention results in a particularly compact design. Many of the components are arranged coaxially with the Xxe2x80x94X axis and/or rotated thereabout. Owing to the coaxial arrangement of the components, which largely prevents shear forces in the transmission, the transmission according to the invention is of small overall dimensions compared to transmissions with variators that have parallel shafts or a countershaft. This is of particular importance in the context of the limited installation space available in vehicles due to necessary ground clearance or the confined transmission tunnel.
In an arrangement according to the invention, certain positions of the toroid variator result in two different input speeds of an (epicycloidal) gear train on the output side, to which the drive speed in particular and the output speed of the variator are fed, for example different input speeds for at least one planet carrier and one sun gear. The input speeds have a different direction of rotation. The different input speeds produce different speeds acting on an epicycloidal gear train or the first planet gear thereof, and a resultant instantaneous center of the planet gear.
According to the operating point of the variator the instantaneous center migrates, especially radially to the Xxe2x80x94X axis. An arrangement of the epicycloidal gear train through an appropriate choice of diameters and transmission ratios, so that engagement of the planet gear or a further planet gear operatively connected thereto (for one operating point of the variator) occurs at the instantaneous center of the (first or second) planet gear, results in a static output element (for this operating point). A similar configuration is possible with a different arrangement of the epicycloidal gear train, for example with double and/or stepped planet gears.
A xe2x80x9creversing gear trainxe2x80x9d is hereinafter taken to be a transmission stage with a reversal of the direction of rotation direction of an input speed to the output speed. For example, the reversing gear train is configured with two intermeshing planet gears arranged between sun gear and internal gear, especially with a transmission ratio of i=xe2x88x921.
The arrangement according to the present invention means therefore that for one variator position the speed of the output shaft is zero, which can be used when the driver requires the vehicle in the stationary position. Slight variations of the operating point of the variator produce large reductions in the drive speed, which results in high starting torques.
With the configuration according to the invention, a starting element such as, for example, a hydrodynamic torque converter and any additional torque converter lockup clutch can be dispensed with. This results in a short overall axial length, a small design volume, a low weight of the transmission according to the invention and fewer components. There are no torque converter losses.
In the known prior art engine shaft and propeller shaft have different directions of rotation in forward drive, which necessitates an additional transmission stage for reversing the rotation direction. This leads to problems with installation in series production cars. For example, it is not possible to resort to existing rear-axle transmissions.
With appropriate selection of the geometric/kinematic parameters of the epicycloidal gear train, the present invention makes it possible, according to the position of the variator, to obtain operation of the transmission at inverse output speeds for the same drive direction. Thus eliminates the need for an additional transmission stage to permit a selectable reversal of direction. This is the case particularly where the operating point of the variator for a stationary output shaft does not form the boundary of the variator operating range. Known transmissions need two separate gears for forward and reverse gear, and at least one further shift element. With the arrangement according to the invention, these components can be eliminated.
The transmission in a currently preferred embodiment has two disks of the variator rotating with one another. That is, the drive toroidal disks or output toroidal disks are connected to one another by the planet carrier of the epicycloidal gear train. The planet carrier therefore has a multifunctional use to simplify the overall construction. If the drive and/or output toroidal disks are separately supported, the bearings must absorb axial forces owing to the contact pressure forces acting between the drive and output toroidal disks and necessary for the transmission of force. This is not necessary with the connection by way of a planet carrier according to the invention. For example, the inner disks rigidly connected together and the transmission elements between the disks, such as toroidal disks or (intermediate) rollers, are arranged between the outer disks rigidly connected together, and are braced with one another owing to the axial dimensioning of the connections. The disks with the assigned connecting elements therefore form a self-contained system with forces cancelling one another out.
The bearing can thereby be configured to save overall space, in particular as a purely radial bearing. A further advantage is an improvement in efficiency. Alternatively, or in addition, elements, especially spring or adjusting elements (for example, mechanical, hydraulic or servo elements) for adjusting the tensioning or the axial distance can be used to obtain the necessary pretensioning force.
The outer disks are preferably connected to one another by the planet carrier and any further hollow shafts. A further simplification or reduction in the size of the construction can thereby be achieved. There is no need for coupling of the inner disks by a connecting element carried radially outside the Xxe2x80x94X axis over the inner disks, for example a dished body having a large geometric moment of inertia owing to the large radial distance. Any support for the rollers in relation to the casing, which owing to the dished body has to be led into the other chamber by way of a hollow shaft arranged between the inner shaft and the inner disks, can also be eliminated.
The connection or the power flow passes, for example, from a first outer disk by way of a hollow transmission shaft running radially inside the inner disks, to an outer hollow transmission shaft or drive shaft. Inner and outer transmission shafts are connected, and in particular torsionally fixed to one another, by a planet carrier supporting the planet gear(s), at the same time absorbing at least the axial forces and forces in the circumferential direction of the Xxe2x80x94X axis, for example.
According to a special embodiment of the invention, the rotational movement of the first planet gear or the output shaft is transmitted by at least one further gear to the gearbox output shaft, particularly to achieve a second drive range. The speed increase or reduction obtained by the variator and the epicycloidal gear train can hereby be varied or, in particular, the spread of the transmission adjusted. In this way transmission ranges can be obtained far beyond the limits of current range automatic transmissions. In particular higher starting ratios can be represented compared to the prior art. In addition, an overdrive can be provided to reduce the engine running speed, especially at high speeds. In particular, a sun gear or the second sun gear or an internal gear is braked in relation to the transmission case to achieve a further drive range.
The further transmission is preferably a transmission stage that can be selected by couplings or brakes. At least one further drive range can thereby be achieved through a simple and/or compact construction. In particular, the drive range can be changed at synchronous speed, thereby making possible shifting of the transmission with little, if any, interruption of the tractive force.